The pressure transmitters, which utilize a sealed dividing membrane, or diaphragm, are also referred to as pressure mediators or pressure intermediaries. Such pressure transmitters include a pressure transmitter body and a dividing, or separating, membrane. The dividing membrane is attached to the pressure transmitter body to form a pressure chamber between a top surface of the pressure transmitter body and the dividing membrane. Also included is a pressure canal, which is in communication with the pressure chamber and over which a measuring cell is loaded by means of a transfer liquid with the pressure prevailing in the pressure chamber. To the extent that the pressure transmitter is integrated in a pressure sensor, or in a measuring mechanism thereof, as the case may be, the pressure canal can extend out to a measuring cell chamber. In the case of a pressure transmitter that is arranged separated from a pressure sensor, a capillary line is connected to the pressure canal. The capillary line extends out to the pressure sensor.
When, during the process of measuring, the pressure of the medium rises rapidly, the transfer liquid is pressed out of the pressure chamber into the pressure canal. In doing this, the transfer liquid flows with a high velocity out of the pressure chamber into the narrow entrance of the pressure canal. Because of the Venturi effect, this can lead to such a decrease of the pressure in the area of the entrance that the dividing membrane is sucked locally onto the membrane bed in the vicinity of the entrance, and the entrance is closed. A measuring of pressure is no longer possible in this state, since communication between the pressure chamber and the pressure measuring cell is broken. When the entrance of the pressure canal converges conically, and this contour is impressed upon the dividing membrane, the above effect is reinforced, for, as the dividing membrane approaches the pressure canal, a kind of annular canal arises between the dividing membrane and the pressure canal in the area of the entrance, wherein the available area for liquid flow gets increasingly smaller with the approach of the dividing membrane. The net effect is a positive feedback of the Venturi effect.